Two researchers are being singled out in what are called PGP poisoning or flood attacks that render the authentication tool unusable for victims. The attack uses a long-feared attack vector used against Pretty Good Privacy, the framework used to authenticate and keep email messages private, is being exploited for the first time. In one of the popular implementation packages of OpenPGP, called GnuPG, attackers are exploiting a known defect where a known problem cannot handle extremely high numbers of signatures very well.
Source: https://threatpost.com/pgp-ecosystem-targeted-in-poisoning-attacks/146240/